Sheet conveying device

ABSTRACT

A sheet conveying device for in an image forming apparatus includes a first guide. A second guide faces the first guide to define a sheet conveyance passage therebetween. A driving shaft is mounted on the first guide and carries driving rollers. A supporting shaft extends substantially orthogonal to a sheet conveying direction. Driven rollers are at opposite ends of the supporting shaft and correspond to the driving rollers. A holder holds the supporting shaft so that the supporting shaft can move towards the driving shaft. Urging members are at opposite sides of an axially center of the supporting shaft for pushing the driven rollers against the driving rollers. The holder is attached to the second guide to swing at a pivotal axis extending in the sheet conveying direction, the pivotal axis is on a plane orthogonally passing the supporting shaft at a center thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet conveying device for use in animage forming apparatus.

2. Description of the Related Art

Conventionally, as disclosed in Japanese Unexamined Patent PublicationNo. 5-69980, there has been known a sheet conveying device provided witha plurality of driving rollers aligned in a direction substantiallyorthogonal to a sheet conveying direction, a plurality of driven rollersfacing the driving rollers, and a guide member in which the respectivedriven rollers are mounted. In this sheet conveying device, the drivenrollers are mounted in the guide member in a state that the drivenrollers are independently urged by a spring member.

Further, Japanese Unexamined Patent Publication No. 6-16303 discloses asheet conveying device provided with a supporting shaft extending in adirection substantially orthogonal to the sheet conveying direction, forrotatably supporting driven rollers at opposite ends thereof, and aguide member in which the supporting shaft is mounted. In this sheetconveying device, a center portion of the supporting shaft is madecontact with a projection formed on the guide member, and the centerportion of the supporting shaft is pressed by a holding member in adirection opposite to the projection to thereby allow the supportingshaft to swing at the center portion thereof.

Recently has been proposed a sheet conveying device in which a firstguide member and a second guide member are provided facing each other todefine a sheet conveying passage therebetween. A driving roller ismounted in the first guide member, and a driven roller is mounted in thesecond guide member. However, if the configuration disclosed in JapaneseUnexamined Patent Publication No. 5-69980 or the configuration disclosedin Japanese Unexamined Patent Publication No. 6-16303 is adopted in suchsheet conveying device constructed as above, the following problems canbe seen to rise.

First, in the case of adopting the configuration of Japanese UnexaminedPatent Publication No. 5-69980, the driven rollers are separatelymounted in the second guide member. If the first guide member and thesecond guide member are not parallel to each other, the driven rollersdo not urge uniformly, causing a sheet skew due to the non-uniformurging force.

In order to prevent the sheet skew, it is necessary to raise thestrength of the second guide member to suppress bending of the secondguide member and to raise the production preciseness of the second guidemember to maintain the parallelism between the first guide member andthe second guide member. This causes increases in the cost and theweight.

Second, in the case of adopting the configuration of Japanese UnexaminedPatent Publication No. 6-16303, even if the first guide member and thesecond guide member are not parallel to each other, the driven rollersmounted on the opposite end portions of the supporting shaft arerespectively urged to the driving rollers owing to the swingness of thesupporting shaft. However, in order to make the urging force of therespective driven rollers uniform, it is necessary to make the distancebetween the first guide member and the second guide member constantwhile keeping the parallelism thereof. For this reason, there is stillthe necessity of raising the strength of the second guide member tosuppress the bending of the second guide member and raise the productionpreciseness of the second guide member.

SUMMARY OF THE INVENTION

In view of the above problems, it is an object of the present inventionto provide a sheet conveying device which can keep a sheet from skewingwithout raising the strength and the production preciseness of a guidemember.

According to the present invention, a sheet conveying device forconveying a sheet, which is to be installed in an image formingapparatus for forming an image on a sheet, includes: a first guidemember; a second guide member facing the first guide member so as todefine a sheet conveyance passage therebetween; a driving shaft mountedon the first guide member and carrying driving rollers; a supportingshaft extending in a direction substantially orthogonal to a sheetconveying direction, the supporting shaft rotatably supporting drivenrollers at opposite ends thereof, the driven rollers corresponding tothe driving rollers, respectively; a holder for holding the supportingshaft in such a manner that the supporting shaft is able to move towardthe driving shaft; urging members provided at opposite sides of anaxially center of the supporting shaft for urging the supporting shaftin a direction of pushing the driven rollers against the drivingrollers. The holder is attached to the second guide member in such amanner that the holder is able to swing at a pivotal axis extending inthe sheet conveying direction, the pivotal axis is on a planeorthogonally passing the supporting shaft at a center thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a configuration of a printer in which asheet conveying device according to an embodiment of the presentinvention is installed.

FIG. 2 is a perspective view showing the sheet conveying device seenfrom an upstream of a sheet conveying direction.

FIG. 3 is a perspective view showing the sheet conveying device with afirst guide member and a second guide member being omitted.

FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 2.

FIG. 5 is a cross-sectional view taken along the line V-V in FIG. 4.

FIG. 6 is a perspective view showing the second guide member.

FIG. 7 is a perspective view showing a holder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the best mode of carrying out the present invention isdescribed in detail referring to the drawings.

FIG. 1 shows a printer 10 as an image forming apparatus in which a sheetconveying device 1 according to an embodiment of the present inventionis installed. The sheet conveying device 1 may be installed not only inthe printer 10, but also in other image forming apparatuses, such as acopying machine, a facsimile machine, or a complex machine.

The printer 10 is operable to form an image on a sheet in accordancewith image data sent from a terminal and the like on a way of conveyingthe sheet along a conveyance passage L. The printer 10 includes, in abox-shaped housing 15, an image forming section 13 in which a tonerimage is transferred on the sheet after the toner image is formed on aperipheral surface of the. photoconductive drum 131, a sheet supplyingsection 12 for supplying the sheet to the image forming section 13, anda fixing section.16 for fixing the toner image to the sheet.

The conveyance passage L includes a horizontal portion L1 extendingsubstantially horizontally from front to back and a vertical portion L2uprising substantially perpendicularly from a tail portion of thehorizontal portion L1 so as to be substantially L-shaped in a side view.

The sheet supplying section 12 includes a sheet supplying cassette 121provided beneath the horizontal portion L1 of the conveyance passage L.In the sheet conveying section 12, sheets accommodated in the sheetsupplying cassette 121 are picked up by a picking up roller 12 a, andthe sheet is fed to the horizontal portion L1 of the conveyance passageL one by one by sheet supplying rollers 12 b to 12 e, the sheet fed tothe conveyance passage L is held by registration rollers 12 f, and thesheet is supplied to the image forming section 13 at a predeterminedtiming.

The sheet conveying section 12 includes a manual feeding tray 122detachably mounted in a front portion of the housing 15. In the sheetconveying section 12, it is possible that sheets mounted on the manualfeeding tray 122 are picked up by a picking up roller 12 g, and fed tothe horizontal portion L1 of the conveyance passage L one by one by thesheet supplying rollers 12 c and 12 e.

The image forming section 13 includes a photoconductive drum 131provided in a substantial center of the horizontal portion L1 of theconveyance passage L in the sheet conveying direction, a chargingsection 132 provided above the photoconductive drum 131, a developingsection 133 provided before the photoconductive drum 131 in the sheetconveying direction, a transferring section 134 provided beneath thephotoconductive drum 131, a cleaning section 135 provided after thephotoconductive drum 131 in the sheet conveying direction, a laserscanner unit (LSU) 14 provided above the charging section 132, thecleaning section 135, and the fixing section 16.

The photoconductive drum 131 rotates in a clockwise direction in FIG. 1.After the peripheral surface of the photoconductive drum 131 isuniformly charged by the charging section 132, a laser beam based on theimage data is irradiated by the laser scanner unit 14 onto theperipheral surface of the photoconductive drum 131 via a space betweenthe charging section 132 and the developing section 133 so as to form astatic latent image thereon. Then, toner particles are supplied by thedeveloping section 133 to form a toner image on the peripheral surfaceon which the static latent image has been formed.

The sheet supplied by the sheet supplying section 12 is conveyed whilebeing urged to the photoconductive drum 131 by a transferring roller 134a of the transferring section 134 so that the toner image formed on theperipheral surface of the photoconductive drum 131 is transferred to asurface of the sheet (a transfer-bearing surface), then the sheet isconveyed to the fixing section 16.

Toner particles or residual charge remained on the peripheral surface ofthe photoconductive drum 131 after completion of the transferringprocess is removed by the cleaning section 135.

The fixing section 16 includes a heating roller 16a and a pressingroller 16 b. These rollers 16 a and 16 b hold the sheet on which thetoner image is transferred so as to fix the toner image to the sheet bythe heat and pressure.

The sheet to which the toner is fixed is discharged by a dischargingroller 18 to a discharge section 19 formed on an upper surface of thehousing 15.

In the printer 10 of the present embodiment, a switchback section 17 isprovided between the horizontal portion L1 of the conveyance passage Land the sheet supplying cassette 121 so that an image can be formed onthe both surfaces of the sheet.

The sheet conveying device 1 is mounted between the fixing section 16and the discharging roller 18, and along the conveyance passage L′ ofthe switchback section 17.

As shown in FIGS. 2 to 5, the sheet conveying device 1 includes a firstguide member 8 and a second guide member 9 facing each other having theconveyance passage L or L′ (hereinafter, they are simply called as theconveyance passage L) therebetween.

The first guide member 8 is made of a synthetic resin and the like, andhas a substantially rectangular flat plate extending along theconveyance passage L.

The second guide member 9 is formed by applying a pressing force to asteel plate and the like, and includes a main plate 91 facing the firstguide member 8, and having the substantially rectangular shape, an endplate 92 extending from an end portion of the main plate 91 in the sheetconveying direction (hereinafter, an X-direction) to a direction bearingoff from the first guide member 8 (hereinafter, a downward Z-direction)along a direction substantially orthogonal to the X-direction(hereinafter, a Z-direction) over substantially whole length of the mainplate 91, and side plates 93 respectively extending from opposite endportions in a direction substantially orthogonal to the X-directionalong the conveyance passage L of the main plate 91 (hereinafter, aY-direction) to the downward Z-direction. The conveyance passage L isdefined between the main plate 91 and the first guide member 8.

The sheet conveying device 1 includes two driving rollers 2 spaced awayfrom a center of the conveyance passage L in the Y-direction withsubstantially equal distance, and two driven rollers 4 facing thedriving rollers 2 in the Z-direction.

The driving roller 2 is made of a rubber material and the like, andpenetrated by a driving shaft 3 extending in the Y-direction so that thedriving roller 2 is fixedly attached thereto. The driving shaft 3 isrotatably supported by a supporting member (not shown) mounted on asurface opposite to a surface which faces the conveyance passage L ofthe first guide member 8, and rotated by an un-illustrated drivingsource in the predetermined rotational number. The first guide member 8is provided with a window 82 in a position corresponding to the drivingroller 2, and a part of the driving roller 2 intrudes in the conveyancepassage L through the window 82.

The driven roller 4 is made of a synthetic resin and the like, and has acylindrical shape. The driven rollers 4 are respectively engaged withthe opposite end portions of a circle-bar shaped supporting shaft 5extending in the Y-direction so as to be rotatably supported at oppositeend portions of the supporting shaft 5. The supporting shaft 5 is heldin a holder 6, the holder 6 is mounted on a surface opposite to asurface facing the conveyance passage L of the main plate 91 of thesecond guide member 9. The main plate 91 of the second guide member 9 isformed with a window 95 in a position corresponding to the driven roller4, and a part of the driven roller 4 intrudes in the conveyance passageL through the window 95 so as to be contactable with the driving roller2.

As shown in FIG. 7, the holder 6 includes a peripheral wall 61 extendingin the Z-direction, and having a cross sectional shape of a rectangulartube extending in the Y-direction, and a bottom wall 62 which closes anopening opposite to the main plate 91 of the peripheral wall 61. Theholder 6 has the shape of a container and opens toward a directionopposite to the downward direction of the Z-direction (hereinafter, anupward Z-direction). The size of the holder in the Y-direction isslightly smaller than a distance between the driven rollers 4 so thatthe holder 6 can be disposed between the driven rollers 4. Inside theholder 6, ribs 63 uprise from the bottom wall 62 at positions bit innerside from the opposite end portions in the Y-direction to connect theopposite long walls of the peripheral wall 61 each other.

In the holder 6, substantially U-shaped bearing recesses 61 a and 63 aare respectively formed in short walls of the peripheral wall 61 andribs 63 in a manner of opening toward the upward Z-direction in the viewfrom the Y-direction. The width of the bearing recesses 61 a and 63 a issubstantially the same as a diameter of the supporting shaft 5. Thesupporting shaft 5 is engaged with the bearing recesses 61 a and 63 a soas to be movably supported by the holder 6 in the Z-direction while thesupporting shaft 5 is covered by the holder 6 from the opposite side ofthe driving rollers 2.

A drooping portion 95 a which droops from an edge portion of the window95 downwardly in the Z-direction is provided in an outside of thesupporting shaft 5 in the Y-direction. The drooping piece 95 a faces anend surface of the supporting shaft 5 so as to restrict movement of thesupporting shaft 5 in the Y-direction. The drooping portion 95 a isformed by cutting a portion corresponding to an area of the window 95 ofthe main plate 91 and bending the same toward the downward direction ofthe Z-direction when the window 95 is formed.

Compression springs 7 are respectively provided in a space between therib 63 and the short wall of the peripheral wall 61. In a case where thesupporting shaft 5 is held in the holder 6, the opposite sides of theaxially center of the supporting shaft 5 are urged by the compressionsprings 7 in the upward direction of the Z-direction so as to urge thedriven rollers 4 against the driving rollers 2. A cylinder-shaped guidemember 62 a for guiding the compression springs 7 projects from thebottom wall 62 in a position between the rib 63 and the short wall ofthe peripheral wall 61.

Projecting portions 66 which project in the upward direction of theZ-direction from the peripheral wall 61 are respectively provided at thecenter of the long walls of the peripheral wall 61 in the Y-direction.Ribs 64 which extend in the Z-direction are respectively provided in theboth inner surfaces of the peripheral wall 61 in the X-direction and theprojecting portions 66. The width of the rib 64 in the X-direction isset in such a manner that a space between the ribs 64 is larger than thediameter of the supporting shaft 5. Shaft restrainers 64 a which projectso as to face each other are respectively provided in end surfaces ofthe ribs 64 in the X-direction and end portions in the upward directionof the Z-direction of the ribs 64, thereby keeping the supporting shaft5 from leaving from the holder 6. The supporting shaft 5 can be forciblyplaced in a space between the shaft restrainers 64 a. In other words, ina case of pressing the supporting shaft 5 into the space between theshaft restrainers 64 a from an outside, the peripheral wall 61 iselastically deformed and the both shaft restrainers 64 a are pushedtoward the both sides in the X-directions so that the supporting shaft 5can pass the space between the shaft restrainers 64 a.

Two pivotal holes 65 a aligned in the Z-direction are provided in bothoutside surfaces of the peripheral wall 61 in the X-directions and theprojecting portion 66.

On the other hand, the second guide member 9 includes a pair ofretainers 94 for holding the holder 6 from the both sides in theX-direction at a position corresponding to substantially a center of theconveyance passage L in the Y-direction, namely, substantially a centerin the axial direction of the supporting shaft 5. The retainer 94 isformed by cutting portions aligned in the X-direction of the main plate91 and bending the same toward the downward direction of the Z-directionso as to be opposite to each other, and is elastically deformable in theX-direction. In other words, the retainers 94 can be pressedly widened.When the retainers 94 are released in this situation, the retainers 94can be restored to original positions by restoring force of theretainers 94. A pivotal stem 94 a which extends in the X-direction andcan be engaged with pivotal hole 65 a of a boss 65 of the holder 6projects respectively in both inner surfaces of the retainers 94. Thepivotal stem 94 a is engaged with the pivotal hole 65 a so that theholder 6 can swing about the pivotal stem 94 a.

With the sheet conveying device 1 configured as mentioned above, theholder 6 swings about the pivotal stem 94 a placed in the positioncorresponding to substantially the center in the axial direction of thesupporting shaft 5 so that a parallelism of the driving roller 2 and thedriven roller 4 can be ensured if the second guide member 9 and thefirst guide member 8 are not parallel to each other. Further, thesupporting shaft 5 is urged by the compression springs 7 at the oppositesides thereof with respect to the center in the axial direction, and thedriven rollers 4 supported by the both end portions of the supportingshaft 5 are urged against the driven rollers 2 with the substantialequal urging force so that a sheet skew can be restrained. Thesupporting shaft 5 is held in the holder 6 to be movable in theZ-direction. In a case where the holder 6 vibrates due to a vibrationgenerated in the second guide member 9, the vibration is absorbed by thecompression springs 7, and can be prevented from transmitting to thesupporting-shaft 5 so that the uniformity of the urging force of thedriven rollers 4 can be ensured. In other words, the strength of thesecond guide member 9 can be lowered to thereby reduce the cost andweight. Further, it is not necessary to produce the second guide member9 with a high degree of accuracy to thereby improve the productionyield.

The holder 6 is so formed to cover the supporting shaft 5 from theopposite side of the driving rollers 2 so that the holder 6 can hold thesupporting shaft 5 to be movable in the Z-direction with a simple shape.The holder 6 is provided with the shaft restrainers 64 a for restrainingthe leaving of the supporting shaft 5 so that the holder 6 can betreated as a unit in which the supporting shaft 5 is installed tothereby improve the assembling efficiency.

The supporting shaft 5 can be forcibly placed in the space between therestrainers 64 a so that the supporting shaft 5 can be held in theholder 6 with a simple fingertip operation.

The retainers 94, in an inner surface of which the pivotal stem 94 arespectively projects, are elastically deformable in the X-direction sothat the holder 6 can be mounted on the second guide member 9 with thesimple fingertip operation.

Two pivotal holes 65 a with which the pivotal stem 94 a is engageableare aligned in the Z-direction so that the urging force of the drivenroller 4 can be adjusted only by shifting the position where the pivotalshaft 94 a is engaged with.

Though the shaft restrainers 64 a are provided in the both ribs 64 inthe embodiment, the shaft restrainers 6 a may be provided in only onerib 64.

Further, though the supporting shaft is urged by the compression springs7 in the above embodiment, it is possible to adopt urging means forurging the supporting shaft 5 with the restoring force caused by anelastic deformation.

Further, the pivotal shaft 94 a may project from the both outer surfacesof the holder 6 in the X-direction and the pivotal holes 65 a may beprovided in both inner surfaces of the retainers 94.

The number of driven rollers 2 is not limited to two, but the numberthereof may be four. In this case, the driven rollers 4 can be providedat a position opposite to the central two driven rollers, or two of setincluding the supporting shaft 5 supporting the driven rollers 4 at theopposite end portions thereof and the holder 6 may be aligned in theY-direction. Further, in a case of six driving rollers, three sets ofthe supporting shaft 5 and the holder 6 can be prepared.

As described above, a sheet conveying device for conveying a sheet,which is to be installed in an image forming apparatus for forming animage on a sheet, comprises a first guide member; a second guide memberfacing the first guide member so as to define a sheet conveyance passagetherebetween; a driving shaft mounted on the first guide member andcarrying driving rollers; a supporting shaft extending in a directionsubstantially orthogonal to a sheet conveying direction, the supportingshaft rotatably supporting driven rollers at opposite ends thereof, thedriven rollers corresponding to the driving rollers, respectively; aholder for holding the supporting shaft in such a manner that thesupporting shaft is able to move toward the driving shaft; urgingmembers provided at opposite ends thereof for urging the supportingshaft in a direction of pushing the driven rollers against the drivingrollers, wherein the holder is attached to the second guide member insuch a manner that the holder is able to swing at a pivotal axisextending in the sheet conveying direction, the pivotal axis is on aplane orthogonally passing the supporting shaft at a center thereof.

With this arrangement, in a case where the second guide member and thefirst guide member are not parallel to each other, the holder swings ata position corresponding to substantially the center of the supportingshaft in the axial direction so that the parallelism of the drivingroller and the driven roller can be ensured. Further, the supportingshaft is urged by the urging members at the opposite sides thereof withrespect to the center of the supporting shaft in the axial direction sothat the driven rollers supported at the opposite end portions of thesupporting shaft are urged against the driving rollers withsubstantially the equal urging force to thereby prevent the sheet skew.Further, the supporting shaft is held by the holder so as to be movablein a predetermined direction (a direction in which the driven rollerfaces the driving roller). With this construction, in a case where thevibration generated in the second guide member causes to vibrate theholder, the vibration is absorbed by the urging members and preventedfrom transmitting to the supporting shaft to thereby ensure theuniformity of the urging force of the driven roller. In other words, thestrength of the second guide member can be lowered so that the cost andweight can be reduced by lessening the material, and the second guidemember is not necessary to produce with the high accuracy, therebyimproving the production yield.

It may be preferable that the holder has a bearing recess which isopened toward the driving shaft and in which the supporting shaft isplaced movably toward the driving shaft.

With this arrangement, the holder can hold the supporting shaft to bemovable toward the predetermined direction with a simple configuration.

It may be preferable that the holder has a shaft restrainer in aposition closer to the driving shaft than the supporting shaft placed inthe bearing recess for keeping the supporting shaft from leaving fromthe bearing recess.

With this construction, the supporting shaft is prevented from leavingfrom the bearing recess by the shaft restrainer so that the holder inwhich the supporting shaft is placed can be treated as a unit, therebyimproving the assembling efficiency.

It may be preferable that the shaft restrainer is provided in theopposite sides of the supporting shaft in the sheet conveying direction,and a gap between the shaft restrainer is smaller than a diameter of thesupporting shaft under a specified pressure, but the gap is expandableowing to elastic shifts of the opposite walls when being applied with apressure greater than the specified pressure.

With this arrangement, the supporting shaft can be forcibly placed inthe space between the shaft restrainer so that the supporting shaft canbe held by the holder with the simple fingertip operation.

It may be preferable that the second guide member includes a pair ofretainers which are opposite to each other in the sheet conveyingdirection and are adapted for retaining the holder swingably.

With this arrangement, the holder can be retained swingably with thesimple configuration.

It may be preferable that the pivotal axis is defined by an engagementof a pivotal stem formed on an outer surface of the holder and a pivotalhole formed in an inner surface of the retainer or an engagement of apivotal stem formed on the inner surface of the retainer and a pivotalhole formed in the outer surface of the holder.

With this arrangement, the retainers can hold the holder swingably onlyby engaging the pivotal stem with the pivotal hole.

It may be preferable that the retainer is elastically shiftable in thesheet conveying direction.

With this arrangement, the holder can be forcedly placed in the spacebetween the pair of retainers so that the holder can be mounted on thesecond guide member with the simple fingertip operation.

It may be preferable that a plurality of pivotal holes are provided in adirection parallel with a plane orthogonally passing the respective axesof the driving shaft and supporting shaft.

With this arrangement, the urging force of the driven roller can beadjusted only by shifting the position with which the pivotal stem isengaged.

Further, in a case of the image forming apparatus in which the sheetconveying device is installed, the above effects can be obtained in theimage forming apparatus.

This application is based on patent application No. 2005-213991 filed inJapan, the contents of which are hereby incorporated by references.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within metesand bounds of the claims, or equivalence of such metes and bounds aretherefore intended to embraced by the claims.

1. A sheet conveying device for conveying a sheet, which is to be installed in an image forming apparatus for forming an image on a sheet, comprising: a first guide member; a second guide member facing the first guide member so as to define a sheet conveyance passage therebetween; a driving shaft mounted on the first guide member and carrying driving rollers; a supporting shaft extending in a direction substantially orthogonal to a sheet conveying direction, the supporting shaft rotatably supporting driven rollers at opposite ends thereof, the driven rollers corresponding to the driving rollers, respectively; a holder for holding the supporting shaft in such a manner that the supporting shaft is able to move toward the driving shaft; and urging members provided at opposite sides of an axially center of the supporting shaft for urging the supporting shaft in a direction of pushing the driven rollers against the driving rollers, wherein the holder is attached to the second guide member in such a manner that the holder is able to swing at a pivotal axis extending in the sheet conveying direction, the pivotal axis is on a plane orthogonally passing the supporting shaft at a center thereof.
 2. A sheet conveying device according to claim 1, wherein the holder has a bearing recess which is opened toward the driving shaft and in which the supporting shaft is placed movably toward the driving shaft.
 3. A sheet conveying device according to claim 2, wherein the holder has a shaft restrainer in a position closer to the driving shaft than the supporting shaft placed in the bearing recess for keeping the supporting shaft from leaving from the bearing recess.
 4. A sheet conveying device according to claim 3, wherein the shaft restrainer includes restraining projections on opposite walls of the bearing recess, the opposite walls face each other in the sheet conveying direction, and a gap between the restraining projections is smaller than a diameter of the supporting shaft under a specified pressure, but the gap is expandable owing to elastic shifts of the opposite walls when being applied with a pressure greater than the specified pressure.
 5. A sheet conveying device according to claim 1, the second guide member includes a pair of retainers which are opposite to each other in the sheet conveying direction and are adapted for retaining the holder swingably.
 6. A sheet conveying device according to claim 5, wherein the pivotal axis is defined by an engagement of a pivotal stem formed on an outer surface of the holder and a pivotal hole formed in an inner surface of the retainer or an engagement of a pivotal stem formed on the inner surface of the retainer and a pivotal hole formed in the outer surface of the holder.
 7. A sheet conveying device according to claim 6, wherein the retainer is elastically shiftable in the sheet conveying direction.
 8. A sheet conveying device according to claim 6, wherein a plurality of pivotal holes are provided in a direction parallel with a plane orthogonally passing the respective axes of the driving shaft and supporting shaft.
 9. An image forming apparatus comprising a sheet conveying device provided with: a first guide member; a second guide member facing the first guide member so as to define a sheet conveyance passage therebetween; a driving shaft mounted on the first guide member and carrying driving rollers; a supporting shaft extending in a direction substantially orthogonal to a sheet conveying direction, the supporting shaft rotatably supporting driven rollers at opposite ends thereof, the driven rollers corresponding to the driving rollers, respectively; a holder for holding the supporting shaft in such a manner that the supporting shaft is able to move toward the driving shaft; urging members provided at opposite sides of an axially center of the supporting shaft for urging the supporting shaft in a direction of pushing the driven rollers against the driving rollers, wherein the holder is attached to the second guide member in such a manner that the holder is able to swing at a pivotal axis extending in the sheet conveying direction, the pivotal axis is on a plane orthogonally passing the supporting shaft at a center thereof. 